The present invention is related to a fixation system for bones with a connecting bar having plural through holes and at least one bone screw, insertable into a through hole. Further, the present invention is related to a filler body for a fixation system of the aforementioned kind.
For the stabilisation of broken bones or of bone portions which are instable due to malunions or in the context of surgical cuts, a plate of metal with through holes and bone screws is used since 1886, following a proposal of C. Hansmann. This system has found worldwide acceptance. Today, it is the third important ostheosynthesis method besides to marrow nailing and ostheosynthesis by means of a fixateur externe.
The dimensioning of plate and bone screws, the proper selection of the metals for plate and bone screw with respect to its mechanical properties and its biocompatibility have been intensively investigated since this time by many research teams.
The importance of the non-positive fit between bone screw and plate has been increasingly recognised and implemented in the last 20 years. In the last years, the research of the present inventors has given the result that in a fixation system with plate and angle-stably fixed (i.e. not pivotal in the plate) screws—therefore a non-positive connection of bone screw and plate—the load on the plate is highest on the level of the first bone screw, which is adjacent to the instable bone portion. Thereafter, the load transmission decays further from through hole to through hole. Approximately, the bone screw in the first through hole transmits about 50 to 60% of the forces, the second bone screw about 20 to 30% and the third bone screw about 10 to 20%.
In order to take this fact into account, the solidity of the plate has been changed by adapted broadenings or thickenings of the plate on the level of the individual holes. This is described in WO 01/19264 A, the entire contents of which is incorporated herein by reference. This solution compensates the enfeeblement of the plate by the through hole. However, there is a demand to further improve the solidity of the plate.
Further, plates without broadenings or thickenings are continued to be used. In particular, in the context of the surgical repair of smaller bones, in the region of the hand skeleton for instance, such reinforcements of the plates in the region of the particularly stressed through holes are not advantageous, for reasons of the anatomic conditions. Therefore there is a demand to increase the solidity of plates otherwise, without broadenings or thickenings.
The same is correspondingly valid for other fixation systems, marrow nails for instance.
Departing from this, the present invention is based on the objective to provide or to make possible a fixation system with further or otherwise improved solidity.